Most Recent Weekly Report: 9 June-15 June 2010

On 10 June the Volcano Alert Level and the Aviation Color Code for Sarigan was lowered to Unassigned because no further volcanic activity was noted since the submarine eruption from a vent S of the island on 29 May.

Most Recent Bulletin Report: May 2010 (BGVN 35:05)

Sudden, short-lived, explosive eruption from submarine vent

According to a weekly USGS/CNMI Emergency Management Office (EMO) update on 4 June 2010, an explosive eruption from a submarine vent S of Sarigan Island occurred during 28-29 May 2010. The most energetic phase of the eruption, at 2147 on 29 May, lasted about 10 minutes based on seismic records from nearby Sarigan and Anatahan islands. The eruption sent an ash and gas cloud perhaps as high as 12.2 km altitude. Precursors included two moderate earthquakes and many smaller shocks; an earthquake of ~ M 4.8 accompanied the eruption. The plume drifted S, eventually passing over Guam (350 km SSW), but no fallout was reported there or on Saipan (165 km S).

Evidence of submarine volcanic activity was first observed late on 28 May during aerial observations by Juan Camacho, an EMO technician, who noted an elongate patch of discolored ocean water and possible light-colored floating debris about 8 km S of Sarigan Island. Alaska Volcano Observatory seismologists noted tremor on nearby seismic stations about the same time. Satellite image analysis by the National Weather Service in Guam indicated that the area of disturbance had grown significantly in size prior to the 29 May explosion. Within hours after the eruption, seismic activity began to decline, and after 31 May only a few scattered events were recorded.

The vent's exact location and depth remained uncertain. According to the USGS, the most likely source is the summit area of the South Sarigan seamount ~ 11 km S of Sarigan Island (figure 1). The summit of the conical structure lies at depths less than ~ 500 m below the surface.

Figure 1. Location map showing the volcanic islands of Sarigan and Anatahan, as well as the South and West Sarigan volcanic seamounts. Modified from Embley and Chadwick (2003).

A U.S. Fish and Wildlife Service research crew camped on Sarigan Island reported many felt earthquakes prior to the eruption. An explosion that sounded like thunder accompanied the event. They also heard increasing ocean wave activity during the night. Subsequently, a minor ashfall occurred.

The NOAA West Coast and Alaska Tsunami Warning Center reported that a 5-cm-high tsunami related to this event may have been recorded on a tide gauge in Saipan. According to a news article in the Saipan Tribune, the U.S. Fish and Wildlife evacuated 16 people, mostly scientists, from nearby islands, including eight people from Sarigan.

The USGS reported no evidence of volcanism after the 29 May eruption. Seismicity recorded by the nearest seismometer, on Sarigan Island, had returned to background levels. Nothing unusual was observed in satellite data.

Index of Weekly Reports

Weekly Reports

9 June-15 June 2010

On 10 June the Volcano Alert Level and the Aviation Color Code for Sarigan was lowered to Unassigned because no further volcanic activity was noted since the submarine eruption from a vent S of the island on 29 May.

On 27 May an observer from the Emergency Management Office (EMO) in Saipan photographed an area of discolored ocean water and possible light-colored floating material about 7 km S of Sarigan during an overflight. The area was about 1.6 km long, although the scale was difficult to discern from photographs. Two days later, the area of affected water was about twice the size of Sarigan Island. According to a news article, U.S. Fish and Wildlife evacuated 16 people, mostly scientists, to Saipan from a few area islands, including eight people from Sarigan.

On 30 May a plume of mostly water vapor was seen in satellite imagery rising to a possible altitude of 12.2 km (40,000 ft) a.s.l. and dissipating as it drifted S. The eruption was attributed to a 300-m-deep submarine vent on Sarigan's S flank, about 7 km from the island. Observers on Sarigan reported hearing a loud explosion from the S, and shortly thereafter received ashfall. The Volcano Alert Level was raised to Watch and the Aviation Color Code was raised to Orange. Both seismicity at a single nearby station on Sarigan and subaqueous activity declined after the plume emission. The next day the Volcano Alert Level was reduced to Advisory and the Aviation Color Code was reduced to Yellow.

Bulletin Reports

All information contained in these reports is preliminary and subject to change.

06/1992 (BGVN 17:06)No activity evident

A six-member team of USGS volcanologists visited the Commonwealth of the Northern Mariana Islands 11-27 May 1992 at the request of the CNMI Office of Civil Defense. Gas emission [from Sarigan] was not evident during overflights in an airplane on 13 May and a helicopter on 21 May.

According to a weekly USGS/CNMI Emergency Management Office (EMO) update on 4 June 2010, an explosive eruption from a submarine vent S of Sarigan Island occurred during 28-29 May 2010. The most energetic phase of the eruption, at 2147 on 29 May, lasted about 10 minutes based on seismic records from nearby Sarigan and Anatahan islands. The eruption sent an ash and gas cloud perhaps as high as 12.2 km altitude. Precursors included two moderate earthquakes and many smaller shocks; an earthquake of ~ M 4.8 accompanied the eruption. The plume drifted S, eventually passing over Guam (350 km SSW), but no fallout was reported there or on Saipan (165 km S).

Evidence of submarine volcanic activity was first observed late on 28 May during aerial observations by Juan Camacho, an EMO technician, who noted an elongate patch of discolored ocean water and possible light-colored floating debris about 8 km S of Sarigan Island. Alaska Volcano Observatory seismologists noted tremor on nearby seismic stations about the same time. Satellite image analysis by the National Weather Service in Guam indicated that the area of disturbance had grown significantly in size prior to the 29 May explosion. Within hours after the eruption, seismic activity began to decline, and after 31 May only a few scattered events were recorded.

The vent's exact location and depth remained uncertain. According to the USGS, the most likely source is the summit area of the South Sarigan seamount ~ 11 km S of Sarigan Island (figure 1). The summit of the conical structure lies at depths less than ~ 500 m below the surface.

Figure 1. Location map showing the volcanic islands of Sarigan and Anatahan, as well as the South and West Sarigan volcanic seamounts. Modified from Embley and Chadwick (2003).

A U.S. Fish and Wildlife Service research crew camped on Sarigan Island reported many felt earthquakes prior to the eruption. An explosion that sounded like thunder accompanied the event. They also heard increasing ocean wave activity during the night. Subsequently, a minor ashfall occurred.

The NOAA West Coast and Alaska Tsunami Warning Center reported that a 5-cm-high tsunami related to this event may have been recorded on a tide gauge in Saipan. According to a news article in the Saipan Tribune, the U.S. Fish and Wildlife evacuated 16 people, mostly scientists, from nearby islands, including eight people from Sarigan.

The USGS reported no evidence of volcanism after the 29 May eruption. Seismicity recorded by the nearest seismometer, on Sarigan Island, had returned to background levels. Nothing unusual was observed in satellite data.

Sarigan volcano forms a 3-km-long, roughly triangular island. A low truncated cone with a 750-m-wide summit crater contains a small ash cone. The youngest eruptions produced two lava domes from vents above and near the south crater rim. Lava flows from each dome reached the coast and extended out to sea, forming irregular shorelines. The northern flow overtopped the crater rim on the north and NW sides. The sparse vegetation on the flows indicates they are of Holocene age (Meijer and Reagan, 1981).

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Synonyms

Savigan

The 3-km-wide, roughly triangular Sarigan volcano is seen here in an aerial view from the NE. The flat area at the right consists of a low truncated cone with a 750-m-wide summit crater that contains a small ash cone. The youngest eruptions produced two lava domes from vents on and near the south crater rim, forming the island's high point at the left. Prehistorical but Holocene lava flows from the dome complex reached the coast at the left center and also formed the peninsula at the extreme left.

Photo by Dick Moore, 1990 (U.S. Geological Survey).

The 3-km-wide, roughly triangular Sarigan volcano is seen here from the east during a 2003 NOAA expedition to the Marianas Islands. A low truncated cone with a 750-m-wide summit crater forms the flat area at the right and contains a small ash cone. The youngest eruptions produced two lava domes from vents on and near the south crater rim, forming the island's high point at the left part of the summit. Prehistorical but Holocene lava flows from the dome complex formed the peninsula at the extreme left.

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.

EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).